[0001] The present invention relates to a paving element comprising an at least substantially
block-shaped body of a composition comprising concrete and having a cover layer differing
therefrom at least in respect of colour, structure and/or material. The present invention
also relates to a method for manufacturing a paving element.
[0002] Paving elements are applied on a large scale as paving for roads, pavements, squares,
patios and the like. The concrete paving stones or tiles applied here comprise a cement-bound
body to which additives such as gravel and sand are added in order to impart strength
and durability, as well as a pigment which serves as colouring agent in the stone
to be finally formed. Within the context of the present invention the term block-shaped
should otherwise be broadly interpreted such that it is understood to mean not only
rectangular beam-shaped bodies, but also other geometric shapes and fantasy shapes.
[0003] A paving element of the type described in the preamble is for instance known from
the American patent
US 6,079,900. The stone described herein comprises a basic body comprising concrete to which a
synthetic cover layer of thermoset-bound granules of rubber and/or a plastic is adhered
at a raised temperature and pressure.
[0004] Known in addition from German patent application
DE 103 11124 is a paving element wherein a cover layer of thinly liquid fluid concrete, which
can be made in a block pattern of differing colours, is cast in a mould before further
filling the mould with a concrete mortar in order to form the basic body therefrom.
The pattern of the cover layer is maintained here by means of narrow separating strips
between successive block parts.
[0005] A drawback of these and other conventional concrete paving stones and tiles is that
they are far from being CO
2-neutral. The production of the Portland cement often used here requires a large amount
of heat which is generated by combustion of fossil fuels such as oil, gas, coal and
brown coal. The synthetic pigments usually used in concrete stones are moreover of
chemical nature and therefore have an environmental impact.
[0006] The present invention has for its object, among others, to provide a paving element
which to at least considerably greater extent is environmentally-friendly.
[0007] In order to achieve the stated object a paving element of the type described in the
preamble has the feature according to the invention that the cover layer is at least
substantially free of artificial additives and that the cover layer comprises one
or more pigments and/or natural stone granulate, which one or more pigments and/or
natural stone granulate have been extracted from nature. By thus applying a pigment
and/or natural stone granulate only in the cover layer, the use thereof can be limited
to a minimum while, once applied in a paving, a desired aesthetic appearance is nevertheless
wholly achieved. Furthermore, according to the invention use is made in the cover
layer of at least substantially only a purely natural pigment, i.e. a pigment extracted
directly from the natural environment and so having no (additional) impact at all
on the environment when it is returned thereto.
[0008] A preferred embodiment of the paving element has the feature according to the invention
that the cover layer comprises cement to which at least one natural pigment is added.
The paving element thus comprises a cement-bound cover layer into which the pigment
has been incorporated. Other additives, such as stone chippings and sand, can optionally
also be added thereto. A further particular embodiment of the paving element according
to the invention has in this respect the feature that the cover layer comprises cement-bound
natural stone granulate. The natural stone material thus applied in the cover layer
imparts a particularly attractive aesthetic quality thereto, while the use of at least
mainly purely natural raw materials in this case also limits the environmental impact
to a minimum.
[0009] Not only the origin but also the extraction of the pigment is advantageously as CO
2-neutral as possible. With a view thereto a further particular embodiment of the paving
element according to the invention has the feature that the pigment comprises natural
iron oxide, in particular iron oxide from Zaragoza extracted by opencast mining. Compared
to mining, opencast mining requires considerably less effort, and so less use of fossil
fuels.
[0010] In a further preferred embodiment the paving element according to the invention has
the feature that the top layer comprises granular olivine. In the form of fine granules
olivine has the capacity to convert carbon dioxide to magnesium(bi)carbonate in a
humid atmosphere. Natural olivine also has the property that it binds with heavy metals
without leaching. The cover layer applied in the paving element according to the invention
thus even makes a positive contribution toward the environment. A considerable, active,
environmentally-friendly surface can thus be created by covering entire road surfaces
therewith.
[0011] Not only the origin but also the extraction of the olivine is advantageously as CO
2-neutral as possible. With a view thereto a further particular embodiment of the paving
element according to the invention has the feature that the top layer is at least
substantially wholly composed of bound granular olivine, in particular olivine from
Norway extracted by opencast mining. Compared to mining, opencast mining requires
considerably less effort, and so less use of fossil fuels.
[0012] Particularly advantageous results are achieved with a particular embodiment of the
paving element according to the invention characterized in that the granular olivine
mainly comprises granulate with a particle size greater than 0 millimetres and smaller
than or equal to 3 millimetres. This particle size is on the one hand small enough
to provide a relatively large reactive surface on which CO
2 can react, and is on the other large enough not to comminute completely, and so disappear,
within a lifespan normally projected for the paving element.
[0013] Calculations show that a paving element according to the invention thus enriched
with olivine is able, subject to the olivine content thereof, to convert a quantity
of CO
2 per square metre. The top layer usually comprises between 11 and 14 kg of olivine
and, based on a reactivity of about 1.25 kilogram of CO
2 per kilogram of olivine, can therefore convert 13.75 to 17.5 kg of CO
2. It is likewise possible to calculate that the production of a square metre of conventional
paving elements of concrete requires a CO
2 impact in the order of 20 kg/m
2. This impact is thus compensated to a significant extent as a result of the invention.
[0014] The CO
2 impact of concrete is associated to a significant extent with the production of the
Portland cement usually applied therein. For clinkering purposes this material has
to be heated to a temperature in the order of 1500 degrees Celsius, this usually being
achieved by the combustion of fossil fuels. A further preferred embodiment of the
paving element according to the invention therefore has the feature that the composition
comprising concrete comprises mainly blast furnace slag cement as binder. Blast furnace
slag cement is produced from blast furnace slags, which are a by-product of the steel
industry and as such do not have any additional environmental impact. The CO
2 impact therefore amounts to no more than about 10 kg/m
2 in respect of the concrete part in the paving elements (owing to the use of blast
furnace slag cement, the use of concrete granulate and sand from a location within
10 kilometres of the production location, and the CO
2-reducing production process), which can be more than compensated by the CO
2 reduction with an olivine-enriched cover layer according to the invention.
[0015] In a further preferred embodiment the paving element according to the invention has
the feature that the composition comprising concrete comprises granules of reused
concrete. By thus making use of reused concrete as additive material for the production
of new paving elements, the cement part can be reduced and a further CO
2 reduction thereby achieved.
[0016] The paving element according to the invention can be realized with diverse cover
layers and various finishing treatments, in particular with a closed cover layer,
a washed cover layer, a shot-blasted cover layer, a curled cover layer, a polished
cover layer, a hammered cover layer or a combination thereof. Any appearance can thus
be thereby realized.
[0017] The invention also relates to a method for manufacturing a paving element wherein
concrete is composed of cement, water and at least one additive, a mould is partially
filled with the concrete, a covering mortar is composed of cement, water and one or
more additives, including at least one purely natural pigment and/or natural stone
chippings, the mould is further filled with a cover layer of the covering mortar and
the thus formed body is cured. Possible additives are for instance sand, gravel, concrete
granulate and limestone meal. Blast furnace slag cement is preferably used here for
the cement, concrete granules for reuse and locally extracted sand and recycled water
are used as additive. The concrete is hereby largely made up of recycled substances
or residual materials, and has a minimal environmental impact.
[0018] In a preferred embodiment the method according to the invention has the feature that
the at least one additive for the concrete is preheated before it is mixed with the
cement and the water, and a further embodiment of the method more particularly has
the feature that the additive is preheated with steam. It has been found that with
such a measure the method can be performed to relatively low ambient temperatures,
while blast furnace slag cement is used as binder for the concrete instead of or in
addition to the Portland cement which has considerably more of an environmental impact.
The preheating of the additives, such as sand and gravel, in particular provides here
for sufficient heat in the concrete mixture so that the temperature thereof lies above
the activation temperature of blast furnace slag cement. It is therefore recommended
that in a further preferred embodiment of the method blast furnace slag cement is
at least mainly applied for the cement. Blast furnace slag cement is a by-product
of the steel industry, so that a separate heating process is not required therefor,
which would otherwise result in an additional CO
2 impact on the environment. Blast furnace slag cement with a high percentage of blast
furnace slags (such as for instance CEM III A+B) is particularly suitable.
[0019] A further particular embodiment of the method has the feature according to the invention
that olivine granulate is applied as additive for the cover layer and that the cover
layer is subjected to a surface treatment, in particular a washing, before the body
is wholly cured. Olivine has the useful property that it converts carbon dioxide into
magnesium bicarbonate, which in turn serves as fertilizer and soil improvement. Owing
to the surface washing, sufficient olivine is exposed to the air in the final end
product to enable this property to be utilized to the full. The olivine does not however
have to be washed, it can also be applied in a closed cover layer.
[0020] In a further preferred embodiment the method according to the invention has the feature
that the body is air-cured in an atmosphere saturated with water vapour and at a raised
temperature above 30 degrees Celsius, particularly at a temperature of around 40 degrees
Celsius. It has been found in practice that such a drying of the stones results in
a considerable reduction in the overall drying time and in a particularly durable
stone quality.
[0021] The invention will now be further elucidated on the basis of several exemplary embodiments
and an accompanying drawing. In the drawing:
- figure 1
- shows a first exemplary embodiment of a paving element according to the invention
with a cement-bound cover layer into which a natural pigment has been incorporated;
- figure 2
- shows a second exemplary embodiment of a paving element according to the invention
with cover layer which is composed substantially wholly of natural olivine grit; and
- figure 3
- shows a schematic view of a production environment for performing an embodiment of
the method according to the invention.
[0022] The figures are otherwise purely schematic and not drawn to scale. Some dimensions
in particular may be exaggerated to greater or lesser extent for the sake of clarity.
Corresponding parts are designated as far as possible in the figures with the same
reference numeral.
[0023] Figure 1 shows a first exemplary embodiment of a paving element according to the
invention. In this embodiment paving element 1 has a block-shaped body 11 with a high
percentage of recycled concrete. Situated on block-shaped body 11 is cover layer 12
which comprises cement-bound chippings, for instance a natural stone granulate or
a mixture thereof, into which an purely natural pigment is incorporated. In this exemplary
embodiment the pigment is natural iron oxide from Zaragoza extracted by opencast mining.
This pigment is purely natural and free of chemicals. Because the pigment is incorporated
in micronized form into cover layer 12, it has a consistent colour. The part of block-shaped
body 11 located under cover layer 12 is substantially free of pigment. Paving element
1 has a light-fastness of 8 (on a scale of 1-8) and a weather-fastness of 5 (on a
scale of 1-5).
[0024] Figure 2 shows a second exemplary embodiment of a paving element according to the
invention. In this embodiment paving element 2 has an H-shaped block body 21 with
a high percentage of recycled concrete. Situated on block-shaped body 21 is a cover
layer 22 which in this case is composed at least substantially wholly of bound, granular,
pure olivine from Norway extracted by opencast mining. In addition to cover layer
22 having a CO
2-reducing effect and binding heavy metals, cover layer 22 is moreover colour-fast,
wear-resistant, durable and aesthetically particularly attractive.
[0025] The olivine is in cover layer 22 in the form of granulate with an average grain size
of larger than 0 and smaller than or equal to 3 millimetres. 75-100% of the additive
used for layer 22 consists of this material, which is able to break down up to 25%
more than its own mass of carbon dioxide. A paving laid with the shown paving elements
can thereby typically remove in the order of 13.75 to 17.5 kilograms of carbon dioxide
per square metre during its projected lifespan. By making use in the production thereof
of reused concrete, blast furnace slag cement with a high percentage of blast furnace
slag and sand from a distance within 10 kilometres of the production location, the
carbon dioxide impact associated with the production process can even be kept below
these values, whereby the paving element according to the invention can make an active
contribution toward a global CO
2 reduction. The main features of such a manufacturing process will be described below
with reference to figure 3.
[0026] The installation shown in figure 3 comprises a number of storage silos having therein
cement (11), sand (12), broken concrete (13) and gravel (14) as the most important
components for concrete production. The cement comprises here a high content, up to
100%, of blast furnace slags, which are available on a large scale as a by-product
of the heavy metal industry. More importantly, this material, in contrast to Portland
cement, needs no so-called clinkering, so that the separate heating and combustion
of fossil fuels otherwise necessary for this purpose are avoided. The use of broken
concrete as additive material instead of pure gravel moreover allows a smaller cement
portion here.
[0027] Situated at the bottom of the silos (12, 13, 14) for the additives for the purpose
of enhancing the later concrete activation are steam lances (15), with which the material
is heated to an increased temperature before it is removed from the silo. The production
can hereby also take place at moderate ambient temperatures, such as outside in winter
in northern regions.
[0028] A mixture of 60% sand, 20% broken concrete, 5% gravel, 13% blast furnace slag cement
and 2% limestone meal is mixed with water in a first mixer (21). Used as water here
is pumped-up groundwater, in addition to as much process water as possible recovered
from previous production runs and filtered. The sand used is preferably extracted,
if possible, in the immediate vicinity, for instance within 10 kilometres, of the
installation so that transport costs and the associated CO
2 emission are limited to a minimum. Thus created is a concrete mixture with a minimal
environmental impact which is pumped to a first dosing unit (31).
[0029] According to the invention paving elements are embodied with a top layer differing
from the base. The installation comprises for this purpose a set of further storage
silos (41, 42), respectively for natural olivine and natural pigment. The olivine
comprises here pure olivine extracted in Norway in opencast mining and having a grain
size greater than 0 millimetres and smaller than or equal to 3 millimetres. The pigment
is likewise purely natural, and originates in Zaragoza. It comprises substantially
iron oxide and is extracted in opencast mining. The pigment can be supplied in red
or black. A number of pigment silos (42) can be applied if desired, each for a separate
colour, from which it is possible to dose and mix in order to obtain different shades.
[0030] A mixture of pigment and/or olivine is fed together with a portion of cement to a
second mixer (22) and bound therein to form a covering mortar with a set quantity
of water. In this embodiment the covering mortar comprises pure cement-bound olivine
without further addition of pigment. This mortar is pumped to a second dosing unit
(32).
[0031] Plastic planks (50) are supplied on an endless conveyor belt (60) under the first
and second dosing units (31, 32), usually referred to as filling carriages. In the
first instance typically 90% of a mould is filled with concrete mortar from the first
dosing unit (31) and then vibrated in order to compact the concrete therein. The vibrating
device applied here is not further shown in the figure.
[0032] Not shown in this figure is that an up and downward moving upper mould (die) and
a lower mould are present between the filling carriages (31, 32). This is placed on
the plastic planks and repeatedly strikes a plastic plank with the stones thereon.
The mould thus remains in the machine and only moves downward when it is about to
be filled.
[0033] The mould is then carried under the second dosing device (32) or, conversely, the
second dosing unit is carried above the mould in order to further fill the mould therefrom
with a cover layer of cement-bound pure olivine granulate. The whole is then vibrated
again in order to also compact the cover layer and impart a good adhesion to the concrete
lying below.
[0034] The concrete body now has handling strength but is not yet cured. In this state the
whole is carried under a spraying device (70) with which water is sprayed under increased
pressure onto the cover layer in order to remove excess cement from the top layer.
In the thus washed cover layer the olivine applied therein is thus exposed to air
so as to enable optimal contact therewith. Furthermore, the attractive natural appearance
of pure olivine is in this way shown to its best advantage.
[0035] Once the enclosing parts of the mould have been removed, the thus formed stones are
dried in a drying chamber. The stones already have handling strength and retain their
shape. The drying is performed in a conditioned environment at an increased temperature
of 30-40 degrees Celsius. In this embodiment a temperature of about 40 degrees is
maintained. After a curing time of no more than 8-10 hours the stones are ready. Drying
in a normal drying chamber would require a considerably longer drying time of more
than 24 hours, whereby the method also provides a significant improvement in this
respect.
[0036] Although the invention has been further elucidated above with reference to only a
single embodiment, it will be apparent that the invention is by no means limited thereto.
On the contrary, many other variations and embodiments are possible within the scope
of the invention for the person with ordinary skill in the art.
[0037] A skilled person will thus appreciate that the block-shaped body can be embodied
in diverse dimensions and shapes, such as for instance small or large polygonal or
round embodiments and numerous fantasy shapes. Other natural pigments can further
be applied so that for instance red, black, yellow and other colours of cover layer
can be obtained. Natural pigments or olivines extracted at other locations may also
be particularly suitable and provide possible variations in appearance or properties.
A skilled person will also appreciate that a non-sprayed closed top layer will also
be very effective.
1. Paving element comprising an at least substantially block-shaped body of a composition
comprising concrete and having a cover layer differing therefrom at least in respect
of colour, structure and/or material, characterized in that the cover layer is at least substantially free of artificial additives and that the
cover layer comprises one or more pigments and/or natural stone granulate, which one
or more pigments and/or natural stone granulate have been extracted from nature.
2. Paving element as claimed in claim 1, characterized in that the cover layer comprises cement to which at least one natural pigment is added.
3. Paving element as claimed in claim 2, characterized in that the pigment comprises natural iron oxide, in particular iron oxide from Zaragoza
extracted by opencast mining.
4. Paving element as claimed in one or more of the foregoing claims, characterized in that the cover layer comprises cement-bound natural stone granulate.
5. Paving element as claimed in claim 4, characterized in that the top layer comprises granular olivine.
6. Paving element as claimed in claim 5, characterized in that the top layer is at least substantially wholly composed of bound granular olivine,
in particular olivine from Norway extracted by opencast mining.
7. Paving element as claimed in claim 5 or 6, characterized in that the granular olivine mainly comprises granulate with a particle size greater than
0 millimetres and smaller than or equal to 3 millimetres.
8. Paving element as claimed in one or more of the foregoing claims, characterized in that the composition comprising concrete mainly comprises blast furnace slag cement as
binder.
9. Paving element as claimed in one or more of the foregoing claims, characterized in that the composition comprising concrete comprises granules of reused concrete.
10. Method for manufacturing a paving element, wherein concrete is composed of cement,
water and at least one additive, a mould is partially filled with the concrete, a
covering mortar is composed of cement, water and one or more additives, including
at least one purely natural pigment and/or natural stone chippings, the mould is further
filled with a cover layer of the covering mortar and the thus formed body is cured.
11. Method as claimed in claim 10, characterized in that the at least one additive for the concrete is preheated before it is mixed with the
cement and the water.
12. Method as claimed in claim 11, characterized in that the additive is preheated with steam.
13. Method as claimed in claim 10 or 11, characterized in that blast furnace slag cement is at least mainly applied for the cement.
14. Method as claimed in claim 11, 12 or 13, characterized in that olivine granulate is applied as additive for the cover layer and that the cover layer
is subjected to a surface treatment, in particular a washing, before the body is wholly
cured.
15. Method as claimed in any of the claims 11 to 14, characterized in that the body is air-cured in an atmosphere saturated with water vapour and at a raised
temperature above 30 degrees Celsius, particularly at a temperature of around 40 degrees
Celsius.